A small release of gas from the anus, but of a smaller quantity than that of a regular fart. One can release a series of fartlets and achieve the same rank effect as a whole fart.
Justin: "I just let out a bunch of fartlets when I was walking past that guy"
Although usually meaning a small piece of excrement attached to the hairs of your arse, sometimes known as a Clingon, it can also mean someone who is a minor, smelly, unpleasant nuisance that is sometimes difficult to get rid of.
"Malcolm is monopolising the vending machine again, no-one can get him to move."
"God! what a fartleberry!"